Thermal analysis and development of PID control for electronic expansion device of vapor compression refrigeration systems

One of the reasons for replacing conventional expansion devices with electronic expansion valves in vapor compression refrigeration systems is associated with the fact that electronic valves promote savings in energy consumption. However, for the electronic expansion valve to be more efficient its PID controller must be properly tuned. Therefore, a refrigeration prototype of simple cycle by vapor compression, who uses R404A and an ethylene glycol solution as a secondary fluid, with nominal capacity of approximately 1 kW has been developed and analyzed. An optimization strategy of a black box model using Matlab (R) software to tune the PI control was used, while the Ziegler-Nichols method was also used to tune the PID control of the expansion device of the refrigeration prototype system. Developing a strategy to optimize the parameters of PI and PID controls to improve the energy efficiency ratio (EER) of refrigeration systems using superheat and valve opening as input variables is the novel contribution of this paper. The PI and PID control models improved the EER of the refrigeration system by 21% to 32% and the factory-set PI control by 28%, respectively. Applying the Ziegler Nichols method for the PI and PID controls improved the EER by 10-17% and by 24 to 28%, respectively, compared to the factory-configured PI controller. The control parameters found with the discrete linear model provided better energy efficiency than the factory setting of the electronic expansion device and with the first Ziegler-Nichols, the PID control had a better EER than the one with the discrete linear model.".